Organic chemistry lesson 10 ( Classification of Alkykhalides)
Classification of alkylhalides (primary, secondary and tertiary alkyl halides with example.preparations of alkylhalides from alkanes, alkenes, and alcohols
## Classification of Alkyl Halides:
Alkyl halides, also known as haloalkanes, are organic compounds containing a halogen atom (F, Cl, Br, I) bonded to a saturated carbon atom. They are classified based on the number of carbon atoms attached to the carbon bearing the halogen atom:
* **Primary (1°):** One carbon atom is attached to the carbon with the halogen. (e.g., CH₃Cl - Chloromethane)
* **Secondary (2°):** Two carbon atoms are attached to the carbon with the halogen. (e.g., CH₃CH₂Cl - Chloroethane)
* **Tertiary (3°):** Three carbon atoms are attached to the carbon with the halogen. (e.g., (CH₃)₃CCl - Trichloromethane)
## Preparations of Alkyl Halides:
**1. From Alkanes:**
* **Free radical halogenation:** Reaction of alkanes with halogen molecules (Cl₂, Br₂) in the presence of light or heat. This is a non-selective method and can lead to a mixture of products. (e.g., Methane + Cl₂ -> Chloromethane, Dichloromethane, etc.)
**2. From Alkenes:**
* **Electrophilic addition of hydrogen halides (HX):** Addition of HX (HCl, HBr, HI) across the double bond of an alkene. Follows Markovnikov's rule, where the halogen atom gets attached to the more substituted carbon. (e.g., Propene + HCl -> 2-Chloropropane)
**3. From Alcohols:**
* **Reaction with hydrogen halides (HX):** Conversion of alcohols to alkyl halides by replacing the hydroxyl group (-OH) with a halogen atom. Requires a catalyst for primary and secondary alcohols, not for tertiary alcohols. (e.g., Ethanol + HCl -> Chloroethane + H₂O)
* **Reaction with thionyl chloride (SOCl₂):** Effective method for converting primary and secondary alcohols to alkyl halides. (e.g., Ethanol + SOCl₂ -> Chloroethane + SO₂ + HCl)
**Note:** The specific reaction conditions and choice of method depend on the desired alkyl halide and the starting material.
